机警的英文：
know the time of day
understand trap
wit

参考例句：

An oBservant Boy
机警的男孩

A cat is not so vigilant as a dog
猫不如狗机警。

Smart and alert
伶俐机警

An oBservant man
机警的人

An alert or watchful person; a guardian.
机警的或警惕的人;守卫者。

Extremely observant;vigilant.
非常机警的;警戒的

The old nurse was prudent and shrewd
这位老保姆小心而机警。

Living in the oceans presented the sea snake with a host of tricky adaptive challenges.
海洋生活给了海蛇很多机警的适应性的挑战。

An observant shop assistant had remembered exactly what the man was wearing.
有个机警的店员准确记得那个男子的穿着

These are not the only points to which you look for vigilant watchfulness
这些并非是诸位选择机警的看守者的唯一条件。

know是什么意思：
v. 知道，了解，懂得；认识，熟悉；认出；体验；见到过，听到过

Learn not and know not
不学无术

Know/not know what is most important and act accordingly
能[不能]按轻重缓急行事

Do you know that lady?
你认识那位夫人吗？

time是什么意思：
n. 时间；（一段）时光；时机；机会；历史时期；时代；次；回；倍
v. 测定…所花时间；调准；调整；测定…所花时间
adj. 时间的；定时的；定期的；分期的

discrimination time
辨别时间辨别时间

It is time to go.
该走了。

They are not in step with the times.
他们跟不上时代的步伐。

day是什么意思：
n. 一天；白昼，白天；工作日；时代，时期

Things go on day by day.
事情逐日进行着。

Day by day the situation is improving.
情况在一天天地好转。

Like this, day after day.
就这样，日复一日。